Outage probability of multihop transmission over Nakagami fading channels

We present a general analytical framework for the evaluation of the end-to-end outage probability of multihop wireless communication systems with nonregenerative relays over Nakagami fading channels. It is shown that the presented results can either be exact or tight lower bounds on the performance of these systems depending on the choice of the relay gain. More specifically, we obtain a closed-form expression for the moment generating function of the reciprocal of the end-to-end signal-to-noise ratio (SNR) and we then use this expression to calculate the outage probability via numerical inversion of the Laplace transform. Numerical examples show that regeneration is more crucial at low average SNR and for multihop systems with a large number of hops.     

Interference management schemes for multi‐user cooperative wireless networks

Cooperative communication is a promising technique for future wireless networks. It can be used in improving communication reliability and enhancing spectrum efficiency by using the broadcast nature of radio communication and exploiting cooperative diversity. However, its performance gain degrades in the presence of co‐channel interference, which makes it essential to propose interference mitigation schemes. In this paper, we introduce three cooperative communication schemes with interference management for multi‐user cooperative wireless networks. The first scheme (best relay selection) is used as a performance benchmark because it completely avoids the interference problem by using the Frequency‐Division Multiple Access technique. The second scheme (best available relay selection) maximizes the received signal‐to‐noise ratio while keeping the interference levels below a certain threshold, and the third scheme (General Order Relay and User Selection) is based on iterative resource allocation algorithm. We derive exact closed‐form expressions of average bit error probability, outage probability, and average consumed power for the proposed schemes. Simulations are used to validate the analytical results. The results confirm the advantage of the proposed cooperation schemes in enhancing the system performance and improving the interference management. Copyright © 2015 John Wiley & Sons, Ltd.     

Harmonic mean and end-to-end performance of transmission systems with relays

Closed-form expressions for the statistics of the harmonic mean of two independent and identically distributed gamma variates are presented. The probability density function of the harmonic mean of two F variates is also derived. These statistical results are then applied to study the performance of wireless communication systems with nonregenerative relays over flat Nakagami fading channels. More specifically, outage probability formulas for noise-limited systems as well as systems affected by interference are obtained. Furthermore, general expressions for average bit-error rates are also derived. Finally, comparisons between regenerative and nonregenerative systems are presented. Numerical results show that the former systems clearly outperform the latter ones for low average signal-to-noise ratios (SNRs). They also show that the two systems have similar performance at high average SNRs.     

Towards passive cooling solutions for mobile access network

The amount of electricity used by mobile networks has become an important issue in recent years as demand for new services has become more widespread. In 2006, energy consumption of Orange mobile network was estimated at 290?GWh per year. Recent works show that thermal architecture must be improved in order to increase thermal efficiency of buildings, shelters, and outdoor cabinets. This paper shows some new approaches on thermal management for telecom enclosures in order to reduce energy consumption of this network.     

Boiling local heat transfer enhancement in minichannels using nanofluids

This paper reports an experimental study on nanofluid convective boiling heat transfer in parallel rectangular minichannels of 800 μm hydraulic diameter. Experiments are conducted with pure water and silver nanoparticles suspended in water base fluid. Two small volume fractions of silver nanoparticles suspended in water are tested: 0.000237% and 0.000475%. The experimental results show that the local heat transfer coefficient, local heat flux, and local wall temperature are affected by silver nanoparticle concentration in water base fluid. In addition, different correlations established for boiling flow heat transfer in minichannels or macrochannels are evaluated. It is found that the correlation of Kandlikar and Balasubramanian is the closest to the water boiling heat transfer results. The boiling local heat transfer enhancement by adding silver nanoparticles in base fluid is not uniform along the channel flow. Better performances and highest effect of nanoparticle concentration on the heat transfer are obtained at the minichannels entrance.     

Experimental study of void fraction profiles in pool boiling on a vertical surface

An experimental study of saturated nucleate pool boiling of n-pentane on a vertical surface was conducted. The boiling surface is 120 mm high and 60 mm width. Using hot wire anemometer, void fraction profiles were measured along the height, width, and the normal of the heated surface for different heat fluxes. The output signals of the hot wire anemometer were treated in order to characterize the boiling flow. The contribution of long, average, and short bubbles along the width and the height of the heated surface are identified for various heat flux. Three different boiling regimes were defined and the transition heat flux density was determined and compared to the results of Gaertner [5]. The wavelength of vapor waves formed on the heater was measured and is higher than the critical wavelength characteristic of the Taylor instability. The experimental results showed that the wavelength is independent of the heat flux and increased along the heater height. However, the number of the wetting zones decreased because of the waves merging and stretching. The physical mechanisms that triggering critical heat flux were identified.     

Stability of vacuolar betaxanthin pigments in juices from Moroccan yellow Opuntia ficus indica fruits

Pigment stability of yellow juices prepared from Moroccan cactus pear (Opuntia ficus indica) was determined as a function of temperature and pH. The experiments were carried out at temperatures ranging from 80 to 100 °C with juices at pH 3.5, 5 and 6.5. The degree of pigment retention decreased when the temperature increased. The degradation constant rates were determined for thermal degradation rates of pseudo-first order. The Arrhenius plot obtained for the degradation of betaxanthin from the yellow fruits was not linear. Regardless of the temperature treatment, the lowest degradation was obtained for pH 5. Where some stabilizers were tested for the protection of pigments, the results showed that ascorbic acid was a better protective agent at pH 3.5, increasing the protection by 40%.     

Synthesis and structural characterization of a new yttrium phosphate:Na2.5Y0.5Mg7(PO4)6 with fillowite-type structure

A new phosphate, Na2.5Y0.5Mg7(PO4)6 was synthesized as single crystals by the flux method and as a powdered sample by the Pechini technique, and investigated by single crystal X-ray diffraction, charge distribution (CD) and 31P NMR spectroscopy. This compound crystallized in the rhombohedral space group R 3 and its equivalent hexagonal cell had the following parameters: a=1.4976(6) nm, c= 4.2599(7) nm, Z=18. The structure consisted of MgO5, MgO6, YO6, (Na,Y)O8 and NaOx (x=6, 7 and 9) polyhedra which were li...     

A novel hybrid requirement’s prioritization approach based on critical software project factors

Cognition, Technology & Work - Requirements prioritization is essential for development of quality software products. Requirements prioritization helps focus on the most important requirements...